The steel industry produces more waste materials than any other manufacturing business. For example, approximately 120 million tons of steel per year are produced in North America. This, in turn, produces about 12 million tons of waste in the form of slag, dust, mill scale, grindings, shot dust, metallic slag fines, sludges, etc. Over half of this is slag which is recycled into aggregates and road materials. The remainder comprises mainly iron oxide. By recycling such waste for metal recovery, it may be reclassified as secondary material.
Over the last 30 years, the manufacturing sector has been called up to comply with ever more stringent environmental standards. The dusts and sludges are particularly polluted with heavy metals such as lead, zinc, cadmium, chromium, nickel, etc. as a result of processing contaminated scrap metal. Consequently, they have been classified as hazardous.
Numerous processes have been developed to treat and recycle steel mill secondary materials and waste but have fallen short of being a comprehensive solution because they only deal with some of the waste and also are very costly. Some of these processes use plasma arc furnaces, briquetting machines and pelletizing systems.
It is an object of this invention to provide a process for treating steel mill waste inexpensively in one system and producing a product that can be stored safely on site as a non-polluting secondary material suitable for recycling in various furnaces such as electric arc furnaces, basic oxygen furnaces and blast furnaces.